Parabolic SAR explained: calculation, trailing stops and whipsaws

Parabolic SAR is a trend-following indicator that plots a series of dots below price in an uptrend and above price in a downtrend. Each bar, the dot moves closer to price by a growing fraction of the distance, so the trail starts loose and tightens as the trend extends. When price touches the dots, the indicator "stops and reverses" (SAR) to the other side.

Traders use it mainly as a trailing stop that adapts to the age of a move. Its weakness is the flip side of its design: because it is always either long or short, it flips back and forth in sideways markets, and each flip is a small loss. This guide shows exactly how the dots are calculated, walks through a worked example, and explains where it helps and where it hurts.

Where Parabolic SAR comes from

The indicator was introduced by J. Welles Wilder Jr. in his 1978 book New Concepts in Technical Trading Systems, the same book that introduced RSI and the Average True Range. Wilder designed it as a complete stop-and-reverse system: always in the market, long or short, with the stop doubling as the reversal point. Most traders today use it more modestly, as a trailing exit or trend filter rather than a system to follow blindly.

It is built into MetaTrader 4 and 5 (as "Parabolic SAR"), cTrader and TradingView.

How it is calculated

Three ingredients drive the calculation:

• SAR: the current stop level, the dot on the chart.
• Extreme point (EP): the highest high reached during the current uptrend, or the lowest low during the current downtrend.
• Acceleration factor (AF): the fraction of the gap between SAR and EP that the SAR moves each bar.

In an uptrend, the next bar's SAR is:

Next SAR = current SAR + AF × (EP − current SAR)

In a downtrend the same formula applies with EP as the lowest low, so the SAR moves down towards price.

The acceleration factor follows Wilder's default rules:

1. It starts at 0.02 when a new trend begins.
2. Each time price makes a new extreme in the trend direction (a new high in an uptrend, a new low in a downtrend), AF rises by 0.02.
3. It is capped at 0.20.

Two more rules complete it:

• No crossing into the recent bars. In an uptrend, the SAR may not be placed above the low of either of the two previous bars. If the formula would put it there, it is set to that low instead. The mirror rule applies in downtrends.
• Stop and reverse. If price trades through the SAR, the trend flips. The new SAR is set to the previous trend's extreme point, the EP resets to the current bar's extreme, and AF resets to 0.02.

Platforms let you change the starting step and maximum. In MetaTrader they appear as "Step" (0.02) and "Maximum" (0.20).

What the acceleration does

Early in a trend, AF is small, so the SAR creeps towards price and gives the trade room. As the trend keeps printing new extremes, AF grows and the SAR catches up faster. Late in a long move, with AF at 0.20, the dots close one fifth of the remaining gap every bar. That is the "parabolic" curve the name describes: a trail that tightens as the move matures.

Worked example: a long trend, bar by bar

These numbers are illustrative and rounded to keep the arithmetic readable. Imagine EUR/USD has just flipped to an uptrend on a daily chart. The starting SAR is the prior swing low, 1.0950, the extreme point is the first bar's high of 1.1010, and AF is 0.02.

1. Bar 2. Next SAR = 1.0950 + 0.02 × (1.1010 − 1.0950) = 1.0950 + 0.00012 = 1.09512, about 1.0951. Bar 2 makes a new high of 1.1030, so EP becomes 1.1030 and AF rises to 0.04.
2. Bar 3. SAR = 1.09512 + 0.04 × (1.1030 − 1.09512) = 1.09544. Bar 3 makes a new high of 1.1055, so EP becomes 1.1055 and AF rises to 0.06.
3. Bar 4. SAR = 1.09544 + 0.06 × (1.1055 − 1.09544) = 1.09604. Bar 4's high is 1.1050, not a new high, so EP and AF stay the same.
4. Bar 5. SAR = 1.09604 + 0.06 × (1.1055 − 1.09604) = 1.09661. Bar 5 makes a new high of 1.1080, so EP becomes 1.1080 and AF rises to 0.08.
5. Bar 6. SAR = 1.09661 + 0.08 × (1.1080 − 1.09661) = 1.09752. Bar 6 makes a new high of 1.1100, so EP becomes 1.1100 and AF rises to 0.10.
6. Bar 7. SAR = 1.09752 + 0.10 × (1.1100 − 1.09752) = 1.09877, about 1.0988.

Two things stand out. First, after six bars and a 150-pip rally from the original low, the SAR has moved only about 38 pips, from 1.0950 to 1.0988. Early in a trend the trail is very loose. Second, the pace is increasing: the SAR moved about 1 pip on bar 2 and about 12 pips on bar 7, because both AF and the gap have grown.

Now suppose on bar 7 price drops sharply and trades down to 1.0985. That crosses the SAR at about 1.0988, so the indicator flips. In stop-and-reverse terms, the long is closed near 1.0988 and a short is opened. The new SAR, now above price, is set to the old extreme point, 1.1100. AF resets to 0.02 and the EP becomes bar 7's low of 1.0985.

If the long had been entered near 1.1000 when the trend began, the exit near 1.0988 would be a small loss despite the pair having rallied 100 pips above entry at one point. That is the classic complaint about Parabolic SAR: a slow start means early trends give back a lot. Some traders deal with it by using a different initial stop and only switching to the SAR once it has caught up.

Using Parabolic SAR as a trailing stop

The most common use today is as a trailing exit for trades entered by some other method.

• Long trades: keep the stop at or just below the SAR dot and move it up each bar as the dot rises. Exit when price hits it.
• Short trades: keep the stop at or just above the SAR dot and move it down.

Because the dot only moves in the trend direction until a flip, it behaves like a ratcheting stop. The difference from a fixed-pip or ATR trail is that it tightens with the age of the trend rather than staying a constant distance. The trailing stop guide compares methods, and the ATR indicator guide covers the volatility-based alternative.

Some practical points:

• Server versus terminal. Most platforms will not move a broker-side stop to the SAR automatically. You either update it by hand each bar, or use an EA in MetaTrader, which only works while the terminal runs. A VPS is a common workaround.
• Bid and ask. Long stops trigger on the bid and short stops on the ask. Charts usually show bid prices, so a short's stop can trigger at a level that looks untouched on the chart when spreads widen.
• Gaps. A stop is filled at the next available price. Over weekends and around major news, that can be well beyond the SAR. The gap risk guide explains why.

Worked example: position size from a SAR stop

Illustrative figures. You have a 5,000 GBP account and risk 1% (50 GBP) per trade. You consider a long on GBP/USD at 1.2650 with the current SAR at 1.2590, so the stop distance is 60 pips. Assume a pip value of about 7.50 GBP per standard lot at that exchange rate (10 USD converted at roughly 1.33 USD per GBP; check the live value).

• Position size = 50 ÷ (60 × 7.50) = 0.111 lots, rounded down to 0.11 lots.

If you wait until the SAR has tightened to 25 pips before entering, size could rise to 0.26 lots, but you are entering later in the trend, when the dots are accelerating towards price and the chance of a stop-out on a normal pullback is higher. Neither is better by default; that is the trade-off you test. The position size calculator and pip value calculator handle the conversions.

Why Parabolic SAR whipsaws

The indicator assumes a trend is always in progress, one way or the other. Markets often do not trend. In a sideways range:

1. Price drifts up, the SAR flips to long below it.
2. Price stalls and dips, hits the SAR and flips it short.
3. Price bounces, hits the new SAR above and flips it long again.

Each flip in a stop-and-reverse system is a closed trade, usually a small loss, plus the spread and any commission. Ten flips in a choppy fortnight can cost more than a good trend recovers. This is the same problem that affects every trend-following method, from moving average crossovers to breakout systems; it is just very visible with SAR because the dots change sides on the chart.

Ways traders try to reduce whipsaws include:

• A trend filter. Only take SAR signals in the direction of a longer-term moving average or a higher timeframe trend, as described in multiple timeframe analysis.
• A volatility or trend-strength filter. Some use ATR or ADX to skip signals in quiet, directionless conditions.
• Slower settings. A smaller step, such as 0.01, makes the SAR slower to catch up and flip, at the cost of giving back more in trends.
• Not reversing. Using SAR only to exit, and entering new trades by a separate rule, avoids being forced into the opposite trade on every flip.

Each of these adds a parameter, and each parameter is another chance to fit the past. Change one thing at a time and test it out of sample.

The limits of Parabolic SAR

• It is a stop, not a forecast. A flip means price moved against the recent extreme by more than the trail allowed. It does not mean a new trend has begun.
• Its stop distance ignores market structure. The dot might sit just above an obvious support level that a structure-based stop would have placed below.
• Its distance ignores volatility directly. The same settings produce very different behaviour on EUR/CHF and GBP/JPY.
• Early trend exits are loose; late trend exits are tight. That suits some trend shapes and not others.
• Results depend heavily on the market regime. A rule that looks excellent in a trending year can lose steadily in a ranging one. Long test periods across different conditions are essential.

How to test a SAR rule

1. Define the rule exactly, for example: enter long on a daily close above the SAR when price is above the 100-day moving average; exit when the SAR is hit; never reverse.
2. Fix the settings in advance. Test the default 0.02/0.20 and perhaps one alternative chosen before you look.
3. Include all costs: spread, commission, swaps for multi-day holds and a slippage allowance.
4. Test several pairs and years, including long ranges, not just the textbook trend you remember.
5. Look at more than the total. Check the number of trades, win rate, average win and loss, and maximum drawdown. The profit factor and trading metrics guide explains what each tells you.
6. Forward test on a demo before committing money, and keep a journal.

A SAR rule will typically have a low win rate and rely on a few long trends to pay for many small losses. That pattern can be hard to live with psychologically, and losing streaks can be long. The risk of ruin calculator shows how win rate, payoff and risk per trade combine.

Common mistakes

• Reversing on every flip. Wilder's original system was always in the market; most traders are better served using SAR only to exit, and filtering entries.
• Using it in ranges. Check whether the market is trending before relying on a trend tool.
• Moving the stop away from the dot. If you use SAR as your trailing stop, a stop you widen when price approaches is no longer a SAR stop.
• Ignoring the starting distance. Early SAR stops can be far away; size from the actual distance.
• Optimising the step and maximum to the past until the equity curve looks smooth.
• Forgetting spreads and gaps, which make real exits worse than the dots suggest. Leverage magnifies every one of these losses, and most retail CFD accounts lose money.

Frequently asked questions

What does Parabolic SAR stand for?

SAR stands for "stop and reverse". The indicator plots a stop level that trails price and, when hit, flips to the other side of the market. "Parabolic" refers to the curved shape the dots make as the acceleration factor increases during a trend.

What are the default Parabolic SAR settings?

The standard settings are a starting acceleration factor (step) of 0.02, increasing by 0.02 at each new extreme, with a maximum of 0.20. These come from Wilder's original description and are the defaults in most platforms.

Is Parabolic SAR a good stop loss?

It can be a reasonable trailing stop in sustained trends because it tightens as the move matures. It is a poor stop in ranges, where it is hit frequently, and its early distance can be wide. Compare it with structure-based and ATR-based stops on your own trades.

Why does Parabolic SAR keep flipping?

Because it assumes a trend is always under way. In sideways or choppy markets, small moves against the recent extreme are enough to touch the dots, and each touch flips the indicator. Trend filters and slower settings reduce flips but do not remove them.

Can Parabolic SAR be used on any timeframe?

Yes, but noise and costs matter more on lower timeframes. A rule that behaves reasonably on daily charts may flip constantly on five-minute charts, with each flip costing the spread. Test on the timeframe you intend to trade.

Should I combine Parabolic SAR with other indicators?

Many traders pair it with a trend filter, such as a long moving average, or a volatility measure. Combining tools can help, but only if testing shows the combination improves results after costs; adding indicators that are built from the same price data often adds complexity without adding information.